Wheat Embryo Ribonucleates. V. Generation of N2-Dimethylgnanylate When 'Fully Sequenced' Homogeneous Species of Transfer RNA are Used as Substrates for Wheat Embryo Methyltransferases

Abstract

1. When S-adenosyl[methyl-14C]methiomne and various species of transfer RNA are used as substrates for wheat embryo methyltransferases, the principal site of guanylate-N2 methylation can be shown to be a G-residue between the stems of the dihydrouridine and anticodon loops. This common site of guanylate-N2 methylation is referred to as the interstem target site.2. When the interstem target site is the non-terminal G-residue in a G-C-G-C sequence, as in the cases of Escherichia coli tRNA1Leu, tRNAIle, and tRNA3Ser, there is preponderant dimethylation to yield N2-dimethylguanylate.3. When the interstem target site is part of a U-C-G-U sequence, as in the case of E. coli tRNAtMet, there is diminished dimethylation and correspondingly increased monomethylation to yield N2-monomethylguanylate.4. When the interstem target site is the non-terminal G-residue in an A-U-G-G sequence, as in the case of yeast tRNAAsp, there is negligible dimethylation and almost exclusive monomethylation to yield N2-monomethylguanylate.5. The concerted way in which the primary, secondary, and tertiary structures of tRNA molecules might influence the efficacy of these methylations is the subject of a brief discussion. Attention is also focused on the evolutionary and molecular basis for the generally non-random distributions of methylated oligonucleotide sequences in ribosomal and transfer ribonucleates.